Studies on dye loss mechanism of reactive dyeings

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(1)The azo-hydrazone tautomerism (AHT) was analyzed through the enthalpies of formation estimated for ten yellow reactive dyes in their hydrolyzed forms using semiempirical molecular orbital (MO) PM5 and COSMO methods according to the group additivity analysis of the AHT.(2)Photo-oxidative fading of reactive pyrazolinylazo and azobenzene dyes (seven) and of reactive azo dyes derived from J-acid and γ-acid (eleven) was examined by exposing the dyed cellulose films immersed in an aerobic aqueous Rose Bengal solution to a carbon arc. The ease with which the dye was photo-oxidized was determined as k_0, the second-order rate constant of the reaction of the dye with ^1O_2. Using the same procedure to determine the AHT, reported above, the reactivity of the tautomer of dyes toward ^1O_2 was analyzed according to frontier orbital theory. The probable reaction modes are ene and [2+2] cycloaddition towards the double bonds. The k_0-values obtained had a close correlation with the sum of Fukui's electrophilic frontier densities, f_r^<(E)>, at both atoms of the corresponding double bonds, a linear correlation between log k_0 and the sum of f_r^<(E)>, although the correlation lines for the eleven dyes differed from the correlation lines for seven pyrazolinylazo and azobenzene dyes.